What really got us excited for a while, which is quite funny now, was to know whether it was inserted into the chromosome or attached to it. And attached to the chromosome, when you think about it there is no attachment system on the chromosome. We would need, I don't know how we could attach it on tyrosine. There is no tyrosine in the chromosome. It isn't obvious how we can- so, eventually, as soon as the structure of the DNA became clear, which was more or less around the same time, it became obvious that it needed to be inserted. But it really- all that really troubled us.
Basically, it's in fact at that time, we didn't have much data on the chromosome. So an attachment model really wasn't unreasonable.
And we didn't have any DNA, well very little that is. But the attachment. Yes, we favoured the attachment, but very quickly, it slipped through our fingers.
Yes but it isn't much in relation to the results that you obtained.
Yes, but it was very important to see how- because the thing that, what really troubled us at the time, was that there were pieces of chromosome that we could add or cut off. And when we would say that, Ephrussi would say, throwing his arms up- A chromosome cannot be manipulated. And in fact, that was the first thing we started to play with. Up until Campbell showed that it was circular, and that the two circles- that we inserted one circle into another one in a linear way. In a very simple way.
And that aspect, precisely the idea that genetical material couldn't be manipulated, that the chromosome couldn't be manipulated, that it was something that was beyond- it's something that you permanently fought against, because with Monod- you also had to convince him a little-
At first, Monod, didn't like it at all. That's true. He was very quickly- he quickly got into it, but at the beginning he didn't really warm up to the idea of adding things on and taking things out of the chromosome. But he quickly got into it. As soon as he understood it, he was very quick.
On lysogeny, wasn't it also maybe a model for understanding phenomena like cancer?
Yes, a little. Yes, it was also mainly presented by Lwoff and a little by me as a way of understanding cancer. Actually, it didn't really teach us much. The cancer virus probably doesn't work like that. They insert themselves next to a gene that they either activate or inactivate, more than by- otherwise.
Nevertheless, at one point you had made the hypothesis that precisely, this sort of activation phenomenon and gene inhibition through the insertion of the phage could be linked to what was happening in cancer.
Yes, but it was quite easy, until the moment-
Yes, but it was a good anticipation.
Yes, it was one way of seeing it. Well, we really liked it because like the cancer model, it brought a lot of interest to this little phenomenon- of lysogeny.
And isn't it in those years that Andrï Lwoff is going to slightly abandon his work on lysogeny?
Yes he decided that he'd had enough of bacteria, he wanted to start working on real viruses. He and his wife went to the United States for one year, and they went to a series of laboratories that were working on mammal cells and on mammal viruses. He went to see Dulbecco, and three-four other guys like that where he learned and came back with the techniques. And so he started cell cultures and things with viruses, real viruses.
But it's an important moment where we were sort of on the verge of understanding what lysogeny was, what it consisted of. So, eventually he now considered this to be your work?
Yes, afterwards. He took the viruses and left us the- It was an incredible model. The key was to know to what extent lysogeny was or wasn't a real model. Eventually, it was a rather good model, but unfortunately it wasn't as simple as lysogeny.

François Jacob (1920-2013) was a French biochemist whose work has led to advances in the understanding of the ways in which genes are controlled. In 1965 he was awarded the Nobel Prize in Physiology or Medicine, together with Jacque Monod and André Lwoff, for his contribution to the field of biochemistry. His later work included studies on gene control and on embryogenesis. Besides the Nobel Prize, he also received the Lewis Thomas Prize for Writing about Science for 1996 and was elected a member of the French Academy in 1996.

Michel Morange is a professor of Biology and Director of the Centre Cavaillès of History and Philosophy of Science at the Ecole Normale Supérieure. After having obtained a Bachelor in biochemistry and two PhDs, one in Biochemistry, the other in History and Philosophy of Science, he went on to join the research unit of Molecular Genetics headed by François Jacob, in the Department of Molecular Biology at the Pasteur Institute, Paris. Together with Olivier Bensaude, he discovered that Heat Shock Proteins are specifically expressed on the onset of the mouse zygotic genome activation. Since then he has been working on the properties of Heat Shock Proteins, their role in aggregation and on the regulation of expression of these proteins during mouse embryogenesis. He is the author of 'A History of Molecular Biology' and 'The Misunderstood Gene'.